Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session K2: Astrophysics V: Stars and Planets |
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Chair: Michele Zanolin, ERAU Room: PSF101 |
Saturday, October 17, 2015 1:12PM - 1:24PM |
K2.00001: Gaining Insight into Star Formation: Variations in Star Formation Efficiency Kelley Liebst, Paul Scowen Until recently astronomers have used star formation laws to measure the star formation rate and efficiency of galaxies only on global scales because of the poor resolution of available data. We are now capable of producing spatially resolved maps of variations in star formation rate and efficiency that can provide direct insight into the physical processes that govern star formation and assess the short-term nature of bursts of star formation and the longer-term nature of larger-scale events that can dictate the global distribution of stars and the ultimate fate of a galaxy as a whole. It is this tracking of the stellar ecology that is vital for insight into the star formation process, but also to understand the conditions that can result in star and planet formation. We are using narrowband optical, infrared, neutral gas, and molecular gas data from a variety of sources to provide star formation rates and efficiencies on previously inaccessible small spatial scales across a suite of galaxies that represent a range of star formation environments and scales. We are using these data to relate the variations in star formation efficiency we observe to the known local physical conditions and the associated star formation histories for each locale within each galaxy. [Preview Abstract] |
Saturday, October 17, 2015 1:24PM - 1:36PM |
K2.00002: correlation between star formation activity and electron density in local galaxies Tianxing Jiang The electron density is tied to the ionization parameter and also provides information on interstellar medium (ISM) conditions on much smaller scales than those used in the studies of the Kennicutt-Schmidt law. We measure the electron density of the ionized gas using the Sulfur line ratio and the star formation intensity in local star-forming galaxies which are composed of four different samples. The measured electron densities span 2 magnitudes, from \~ 10 $cm^{-3}$ to \~ 1000 $cm^{-3}$. The correlation between star formation intensity and electron density in local galaxies is uncovered. Moreover, we find that the correlation in local star-forming galaxies is consistent with that at $z = 2.5$. This means that the high-redshift and local galaxies with the same star formation intensity have very similar electron density, which is contrary to the conclusion in some previous studies, and thus possibly indicates a consistent star formation law in ionized gas in both low-z and high-z galaxies. [Preview Abstract] |
Saturday, October 17, 2015 1:36PM - 1:48PM |
K2.00003: Characterizing the Stellar Halo of M83 Michael Busch, Eric Bell, Sarah Loebman, Ian Roederer Cosmological simulations of $\Lambda $CDM predict a hierarchical Galactic formation by the accretion of smaller satellite galaxies onto the main galactic plane. We observe far fewer satellite galaxies (\textasciitilde 20) in the stellar halo in the Local Group than predicted by $\Lambda $CDM (\textasciitilde 500). The GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters) survey is the largest study of stellar populations in the stellar halos of 16 nearby disk galaxies using the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). Additionally, the Subaru Telescope on Mauna Kea is a ground-based telescope capable of providing a wide-field survey of the stellar halo. This work characterizes the stellar halo of M83, a Milky Way type galaxy at a distance of \textasciitilde 5 Mpc. We present early results on a method to use GHOSTS as a targeting survey to calibrate Subaru data, using Stellar Locus Regression to calculate color-color cuts and star-galaxy separation in Subaru data. The goal is to characterize the stellar populations, specifically Red Giant Branch (RGB) stars, as they are tracers of the underlying galactic formation. [Preview Abstract] |
Saturday, October 17, 2015 1:48PM - 2:00PM |
K2.00004: Simulating exoplanet hazes with high temperature discharge experiments Ehsan GharibNezhad, James, R. Lyons, David, P. Wright Spectral observations of exoplanets have revealed only a few detections of atmospheric species, and only for hot Jupiters. Most notably, transit spectra have revealed absorption signatures due to Na and K in the visible, and H$_{\mathrm{2}}$O and CO have been detected in the IR. The most consistent feature observed in transit spectra is a flat or nearly flat absorption spectrum from the mid-IR into the visible. Observations of GJ1214b (a superearth) exemplify this, with observations over 60 HST orbits yielding a completely flat spectrum. The most likely explanation for a flat absorption spectrum is the presence of clouds or photochemical hazes. Here we explore the latter via laboratory experiments. We heat a mixture of gases (H$_{\mathrm{2}}$, H$_{\mathrm{2}}$O, CH$_{\mathrm{4}}$, N$_{\mathrm{2}}$, and H$_{\mathrm{2}}$S) in a fuzed quartz tube to 800 K in a tube furnace. Tungsten electrodes are used to generate 60Hz plasma discharge with an arc nearly spanning the width of the furnace. Thin films of particulates formed in the hot discharge are collected on fuzed quartz plates positioned beneath the tips of the electrodes. Measurements of the IR, UV-vis, and optical properties of the thin films are in progress, and will be reported at the meeting. [Preview Abstract] |
Saturday, October 17, 2015 2:00PM - 2:12PM |
K2.00005: Adaptive Optics Imaging of Exoplanet Host Stars Miranda Herman, Mason Waaler, Kimberly Ward-Duong, Jennifer Patience With the 6.5m MMT observatory on Mt. Hopkins we obtained high angular resolution images of 12 exoplanet host stars. The targets are all systems with exoplanets in extremely close orbits such that the planets transit the host stars and cause regular brightness changes in the stars. The level of brightness change is used to infer the radius and density of the planet (radial velocity methods are used to determine the planet's mass), but the values can be incorrect if the light from the host star is the combined light of a pair of stars in a binary system. The adaptive optics images were used to determine if any of the host stars had a previously unknown second star at a small enough separation that would affect the interpretation of the planet properties. After analysis, companions were identified around five of the twelve targets. This indicates that the brightness measurements of these host stars are in fact the combined brightness of their systems. Correcting for this has the effect of increasing the inferred radius of the planet and therefore decreasing its density, which provides insight into its composition and the ways in which stellar properties impact planetary characteristics. [Preview Abstract] |
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